A high-refractivity low-dispersion optical glass is much demanded as optical element materials such as various lenses. For example, it can constitute a compact and highly functional optical system for correcting chromatic aberration when combined with a high-refractivity high-dispersion lens.
Further, when the optical function surface of a high-refractivity low-dispersion lens is rendered aspherical, various optical systems can be functionally enhanced and downsized.
A precision press-molding method is known as a method of efficiently producing optical elements made of a glass such as an aspherical lens, etc., that require much labor and a high cost when they are produced by grinding and polishing. High-refractivity low-dispersion glasses used in the above precision press-molding method are disclosed in Patent Documents 1 to 3.